A traffic data signal is commonly associated with a path trace identifier, or section trace identifier, which carries information identifying the data signal. The path trace, or section trace, information is normally used to verify network connectivity. Typically, this is achieved by comparing ‘expected’ trace information with ‘received’ trace information. If there is mismatch, then this is an indication of a misconnection.
In an SDH/SONET network, the J1 or J2 byte of the traffic data structure normally serves as the path trace component, while the J0 byte serves as a section trace component. The path trace, or section trace, data itself normally comprises a string of 16 or 64 bytes, being comprised of the contents of 16 or 64 successive instances of the J0, J1 or J2 byte as appropriate.
Conventionally, at a given network element, the path trace, or section trace, string is extracted from an incoming data signal for comparison against an ‘expected’ path trace, or section trace, string which is stored locally. One option is to extract and store the entire incoming trace string, to compare the received string against the ‘expected’ string and to make a match or mismatch decision. Alternatively, as each respective byte of the incoming trace string arrives, it is compared against the corresponding byte in the ‘expected’ string. The latter option obviates the need to store the entire incoming path, or section, trace string. Nonetheless, at least the current incoming path, or section, trace byte and the entire ‘expected’ path, or section, trace string must be stored locally at the network node. This represents a relatively large storage overhead. The problem is exacerbated by the fact that the incoming data signal may comprise a plurality of smaller data signals, or channels, in respect of each of which the network element may be required to store a respective ‘expected’ path, or section, trace string. Because of the physical limitations of the network element, it is common that only a limited number of path or section traces can be monitored at any one time. Typically, a relatively small number of path, or section, trace monitors are rotated in order to provide coverage of all channels.
It would be desirable, therefore, to provide more efficient path, or section, trace monitoring which has relatively low storage requirements.